Check in codegen test expectations.

test/codegen/expect/corelib/map_index_test.js

+dart_library.library('corelib/map_index_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__map_index_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const _interceptors = dart_sdk._interceptors;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const map_index_test = Object.create(null);
+  let MapOfB$B = () => (MapOfB$B = dart.constFn(core.Map$(map_index_test.B, map_index_test.B)))();
+  let JSArrayOfB = () => (JSArrayOfB = dart.constFn(_interceptors.JSArray$(map_index_test.B)))();
+  let JSArrayOfMapOfB$B = () => (JSArrayOfMapOfB$B = dart.constFn(_interceptors.JSArray$(MapOfB$B())))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  map_index_test.A = class A extends core.Object {
+    new() {
+    }
+  };
+  dart.setSignature(map_index_test.A, {
+    constructors: () => ({new: dart.definiteFunctionType(map_index_test.A, [])})
+  });
+  map_index_test.B = class B extends map_index_test.A {
+    new() {
+      super.new();
+    }
+  };
+  dart.setSignature(map_index_test.B, {
+    constructors: () => ({new: dart.definiteFunctionType(map_index_test.B, [])})
+  });
+  let const$;
+  let const$0;
+  let const$1;
+  map_index_test.main = function() {
+    let map1 = MapOfB$B().new();
+    map1[dartx.set](const$ || (const$ = dart.const(new map_index_test.B())), const$0 || (const$0 = dart.const(new map_index_test.B())));
+    let map2 = MapOfB$B().new();
+    let list = JSArrayOfB().of([const$1 || (const$1 = dart.const(new map_index_test.B()))]);
+    let maps = JSArrayOfMapOfB$B().of([map1, map2]);
+    for (let map of maps) {
+      expect$.Expect.isNull(map[dartx.get](new map_index_test.A()));
+    }
+  };
+  dart.fn(map_index_test.main, VoidTodynamic());
+  // Exports:
+  exports.map_index_test = map_index_test;
+});